Tracer projectile for rifles



Feb. 10,1970 T. A. DORIS, JR., ET AL 3,

TRACER PROJECTILE FOR RIFLES Filed March 29, 1968 INVENTORJ, THOMAS A. DOR|S,JR.

THOMAS Q. CICCONE 141 $1.! 41.2 ,1. mag/w 8144* 6. PM ATTORNEYS:

United States ate US. Cl. 102-87 2 Claims ABSTRACT OF THE DISCLOSURE The tracer pocket or cavity provided in the rear end of tracer projectiles or bullets is provided with an ablative liner that sublimes or vaporizes with heat as the tracer charge burns and relieves the centrifugal pressure caused by the spin. This lowers the burning rate and prolongs the effect of the tracer charge and the visible trace.

The invention described herein may be manufactured, used and licensed by or for the Government, for governmental purposes, Without the payment to us of any royalty thereon.

The present invention relates to small-arms ammunition and more particularly to tracer projectiles or bullets for use in rifle ammunition. Such projectiles are provided with a central pocket or axial cavity in the rear end from which a charge of pyrotechnic material, or powder mixture, burns to give the visible projectile trace in the air. If the charge burns out too fast the trace is lost before the projectile reaches the target area.

Thus it is an object of the present invention to provide an improved tracer projectile or bullet for firing from guns with rifling, such as small-arms rifles, which will have an increased and effective burning time for a full trace to a target or target area.

It is known that the burning times of pyrotechnic powder mixtures are greatly affected by pressure, that is, the burning rate goes up greatly with increased pressure. It is further known that conventional tracer projectiles or bullets, when fired from a gun with rifling in the bore, which imparts spin to the projectile or bullet, manifest a burning rate which is at least twice that of a statically burning tracer projectile or bullet.

The increase of burning rate during spin has been attributed to slag build-up on the outer or peripheral wall of the tracer cavity due to centrifugal force. This effectively reduces the cavity size and thus increases the ambient pressure on the burning charge. Efforts to significantly decrease the burning rate, that is, to increase the burning time of a given charge, have thus far been met with difliculties, and attempts to accomplish thus by mixture formulation have not been totally effective. Thus the problem of making the tracer charge in tracer ammunition burn for a longer time still remains.

Therefore it is also an object of this invention to provide an improved tracer projectile or bullet structure in which the burning rate of the tracer charge is reduced by control of the ambient pressure thereon.

In accordance with the invention this is accomplished by designing into the tracer pocket or cavity at the rear end of the projectile or bullet, a means or technique for using the above pressure effect to advantage. In essence this involves charging pyrotechnic tracer mixtures as a core into an elongated ablative tracer cavity so that as the tracer core burns the surrounding substance or cavity wall sublimes, vaporizes or otherwise disappears with the heat of combustion at about the same rate as the core of the tracer mixture burns. By this means and technique, the ambient pressure on the burning pyrotechnic mixture is continually relieved as the ablative cavity wall disapice pears, and the burning time can then approach that obtained with a static projectile.

The invention relates to and is particularly adapted for tracer-fuse trains such as used in self-destructing projectiles which are made to explode as the tracer compositions or charge burns down. In this case it is not only desirable but necessary to obtain as long a burning time as possible, consistent with visible trace. Also by this technique it is possible to use tracer mixtures of higher light intensity where previously the burning times of such mixtures would be too short.

The invention will further be understood from the following description when considered with reference to the accompanying drawing, and its scope is defined by the appended claims.

In the drawing, FIG. 1 is a longitudinal side view, in section of a projectile embodying the invention, and FIG. 2 is an end view thereof.

Referring to the drawing, 5 is a projectile or bullet having a cylindrical forwardly-tapered metallic body 6 with a recessed rear or base end 7 fitted with an open elongated axially-extending tracer cavity 8. The forward end or nose cone is only indicated in dotted outline as it does not concern the invention directly and while the interior is provided with a central chamber '9, in the present example, for carrying an explosive charge, as a small cannon shell, for example, it may be solid in regular bullet form. To take the riding it is also fitted with a rotating band 10 of copper or like softer metal, thus to give it the required spin on firing. As a smaller caliber bullet it would have a soft metal coating or a grease groove for lubricant as is understood. Small radial vents or openings 11 may be provided for the cavity 8 to aid in the burning operation.

In any case and as shown in the drawing, the rear end of the projectile is fitted with a deep central cavity for receiving the charge of pyrotechnic tracer mixture, indicated at 12, in a core or column extending from the closed inner end to the open rear end. The latter is sealed with a closure disc 13 which is ruptured upon firing of the propellant in the gun or rifle by which the projectile is launched or fired.

As indicated, the cavity 8 is preferably circular and the outer or peripheral wall its provided with a relatively thick cylindrical liner 14 of ablative material extending along its full length or depth and surrounding the column or core of tracer mixture or charge 12. The liner is relatively thick and for a 0.4" diameter cavity, for example, may be increased to 0.6" diameter so that the liner would be A inch thick.

The ablative liner is one that sublimes with heat, or disappears as by evaporation or vaporization so that it passes off as a gas from the solid state. Ablative materials which have been found to be satisfactory for this liner for the cavity wall are: low-melting metal alloys, such as lead with hardeners such as antimony and bismuth; inert salts, such as sodium or potassium chloride which melts at about 900 F.; or sublimable organic compounds, such as dyes for yellow, red and green smoke flares, for example.

The problem of making the tracer charge burn longer, that is, to insure the trace following through with the projectile over the full flight path to a target, has been met with the tracer projectile construction shown and described as above. When the projectile is fired, an igniter charge or disc 15 is initiated, after rupture of the disc 13, to start burning of the tracer column or core 12 from the rear forwardly as the projectile moves in flight from the rifled gun or launching means.

As the pyrotechnic tracer column burns, the liner 14 sublimes or vaporizes and disappears at approximately the same rate and relieves the centrifugal pressure on the burning mixture and the resultant slag, permitting the latter to expand into the space vacated by the liner or ablative wall of the cavity. This keeps the pressure down in the cavity and slows the burning rate. Thus the trace covers a greater length of the projectile flight. The incandescent slag particles of the mixture or core flow out with the liner gaseous products. In the case of the sublimable organic compounds mentioned, these pass from solid to gaseous state directly and permit the slag thus to expand and flow out of the cavity with lowered pressure.

We claim: 1. A tracer projectile comprising in combination, an elongated metallic body having a tapered forward end and a rear base end containing a central axiallyextending tracer cavity, a relatively-thick cylindrical liner of ablative material comprising a low-melting metal alloy containing lead and hardeners such as antimony and bismuth, said liner extending along the cavity Wall, a charge of pyrotechnic tracer mixture within the cavity and the liner, an igniter charge, and a means for providing a closure for the cavity and a retainer for the said charge, said igniter means being adapted to be initiated by burning propellant in rear of the projectile upon firing, and means providing radial venting of said cavity about said liner. 2. A tracer projectile comprising in combination,

an elongated metallic body having a tapered forward end and a rear base end containing a central axiallyextending tracer cavity, a relatively-thick cylindrical liner of ablative material comprising an inert salt such as sodium or potassium chloride, said liner extending along the cavity wall, a charge of pyrotechnic tracer mixture Within the cavity and the liner, an igniter charge, and a means for providing a closure for the cavity and a retainer for the said charge, said igniter means being adapted to be initiated by burning propellant in rear of the projectile upon firing, and means providing radial venting of said cavity about said liner.

References Cited UNITED STATES PATENTS 2,868,129 1/1959 Johnson et a1. 10287 2,899,291 8/1959 Heiskell 10287 XR 3,236,183 2/1966 Littleford 102-87 FOREIGN PATENTS 564,936 11/ 1932 Germany. 747,669 12/1966 Canada.

ROBERT F. STAHL, Primary Examiner 

